Major changes:
  - when rotating, the top left corner of the rectangle stays in place.
  - ValueViewers get a dc that is pre-rotated/translated for them, i.e. (0,0) is the top-left of the viewer (with ValueViewer::getRotation).
  - moved 'angle' from individual Styles to the Style base class.
  - any rotation angle is now possible. angle is still an int for now.

This warrants a version bump